Vent for floating roof tanks



Aug. 21, 1951 F. D. MOYER ET AL VENT FOR FLOATING-ROOF TANKS 2 Sheets-Sheet 1 Filed June 2, 1945 Aug. 21, 1951 F. D. MOYER ETAL 2,564,711

VENT FOR FLOATING ROOF TANKS Filed June 2, 1945 2 Sheets-Sheet 2 Patented Aug. 21, 1951 UNITED STATES VENT FOR FLOATING RGOFTANKS.

Frederick 1). Meyer and J 01 n W; Allen, Chicago.

31., assignorsto Chicago Bridge & Iron Conipany, ac'orporation of- Illinois Application June 2, 1945, Serial No. 597,248

2 Claims. 1

This invention. relates to a vent for a liquid storage tank, and relates particularly to a vent for a floating roof' tank.

It has been found that where extremely volatile liquids, are to be stored in large quantities, it is desirable to build the storage tankswith floating roofs, so'that the space between the top of the liquid and the top of the tank is'small at all times. By keeping this space small it is found that the volatile liquids are less subject-to evaporation losses. The floating roof floats on top ofthe liquid in the tank, and is provided wit a frictional seal between the roof and-the sides of the tank. In this construction when the tank is; fullthe roof will be up near the top of the tank. i'hen as the tank is emptiedtherobflowers, thereby keeping at all times-substantially the same small space between the top of the liquid" and the roof ofthetank. Because'the liquids in a tank of this type are usually quite volatile; the space above the liquid is sometimes under pressure higher than atmospheric pressurecausedby evaporation of the liquid. Then at other times this space is unde-rvacuum or at pressure lower than atmospheric pressure. In order to relieve-the pressure andvacuuin in the tank it has been proposed to provide a vent that will automatically correct these conditions.

The vents that were proposed in the past were oftentimes-of complex construction and had several moving parts that were subjectedto wear. Many ofthe vents used liquid sealing material that hadtobe renewed from time to time, and it sometimes happened that condensate from the tank froze up and made the vent non-operative. There has never been a completely satisfactory vent that was automatic in operation and that required a minimum of. care and attention. The new vent which is the subject of this invention overcomes the'objections of the old type vents inthatit. is of very simplev ccnstructiQn-,.p cvid automatic sealing of the contents. of; the tank, and is completely, non-freezing. Thenew vent has only one moving part, which is a freely rising cup, and thus requires a very minimumof service and attention. There are no valve seats, and the liquid in the tank provides the only liquid seal necessary. Thenew vent has a positive action for both pressure and vacuum.

The new vent which we have invented is mounted on the floating portion of a floating roof liquid storage tank where pressure and vacuum in the tank cause the roof to rise and fall respectively. This vent comprises broadly a pipe submerged in the liquid in the tank and 2 having one end opento the atmosphere and the other end open tothe interior of the tank above the highestv liquid level. Over the interior end of thepipe there is positioned. invertedcup that is free to move relative to. thepipebut is prevented from ever completely closing the end of the pipe. The vent, beingmounted on the roof, rises and falls with the roof under the forces of pressure and vacuum within the tank.

The invention will be described as related to the typicalembodiinent of the same shown in the accompanying drawings. Of the drawings, l is a plan view of the, new vent attached to. the. roof of a floating roof tank; Fig. 2 is a section elevation taken along line, 22 of Fig, l; 3 is an end elevation of the vent; Fig. i. is a horizontal section taken along line l -t of Fig. 2; and Fig. 5 is a section taken along line. of Fig. 2.

The new vent shown in, the accompanying drawings includes a U-shaped pipe IE3 mounted in inverted position in the roof of the tank with one end I! of the pipe extending above the roof and the other end 52 of the pipe below the roof. The confined end i2 of the pipe is positioned so that at all times it is above the liquid level within thetank. On the open end ll of the pipe there is positioned a loosely fitting cap i3 toprevent rain from falling into the open end. This cap is supported on radial bars is fastened to the and is hingedly mounted so that it may be readily removed for cleaning purposes. Between the cap l3 and the pipe there is located a screen [-5 to prevent dirt andother foreign bodies from entering the open end H of the pipe. On the confined end !2 of the pipe there is mounted a cylindrical housing it that extends abovethe roof of the tank. Within the housing and over the end of the pipe there is positioned an inverted cup ll normally resting on the bottom of the cylindrical housing It. The housing has radial slots [8 in the bottom and the inverted cup I? normally rests on the partitions lilbetweenthe slots. The housing it and the inverted cup H are proportioned so that the cup never completely closes the end i2 oi" the pipe, and the housing is substantially twice as long as thecup. In the sides of the cylindrical housing there are provided a number of slots 2%! that extend downwardly from a point just beneath the roof of the tank. Thetops of these slots are always above the highest liquid level.

In order that excessive loss of vapor from the tank will be prevented there is provided a vapor trap 2| mounted near the top of the confined end |2 of the pipe.- This vapor trap comprises an inverted cup 22 attached to and concentric with the pipe l0. Within the cup 22 there are proijidd a plurality of radial vanes 23 extendin from the pipe tothe sides of the cup 22. These vanes serve to give a large surface upon which vaporarising from the liquid may be condensed, and thus be prevented from escaping from the tank. The condensate on the vapor trap drips back into the tank.

The vent shown is mounted in the roof of the tank near one side of the roof by means of a mounting plate 24 extending from the pipe to the side of the roof and a second mounting plate 25 extending from the cylindrical housing [6 to the side of the roof. The cylindrical housing has a top portion 26 that is bolted to the sides of the cylinder and provided with two handles 21 so that the top may be easily removed for cleaning purposes.

The vent operates as follows: When the space above the liquid in the tank is under pressure greater than atmospheric pressure the roof rises until the liquid level is at the line 28 (Fig. 2). At this point the liquid level is even with the bottom of the inverted cup IT. The vapor pressure thereupon is relieved into the interior of the inverted cup and on out the pipe 10. The vapor flowing around and in the vapor trap 2i tends to condense on the radial vanes 23 and the vapor trap cup 22, and this condensate drips back into the tank. Such a construction serves to reduce materially the product loss normally caused by the escape of vapor. When the interior of the tank is under vacuum the roof sinks until the liquid level is substantially at the line 29. Here the movable inverted cup I! arises within the housing l6 until the bottom of the cup is substantially even with the end 52 of the pipe. This movement Of the inverted cup I! is caused by air pressure operating through the open end ll of the pipe 19 out into the interior of the inverted cup. As soon as the cup has risen to its proper position the air flows past the bottom of the cup into the interior of the tank and serves to relieve the vacuum. At this point of course the vapor trap is immersed in the liquid within the tank. It can thus be seen that on both pressure and vacuum the vent has a positive action that serves to relieve these conditions promptly.

Having described our invention as related to a typical embodiment of the same, it is our intention that the invention be not limited by details of description unless otherwise indicated, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

We claim:

1. In a floating roof tank having a roof adapted to float at various heights above the liquid level with varying vapor pressure in a space beneath the roof, a vent comprising: a substantially vertically arranged U-shaped pipe extending through said roof and having an exterior end open to the atmosphere and an interior end located in said space beneath the roof, said pipe having a first portion extending downwardly through said roof, an intermediate portion normally immersed in the liquid, and a second portion extending upwardly to said interior end;

an inverted cup over the interior end of said pipe, said cup being mounted for free vertical movement relative to said pipe and to said roof with variations in the height Of said roof for limiting the downward movement of said cup to prevent the cup from closing the interior end of said pipe, the lower edge of said cup being normally immersed in the liquid to provides, seal about the interior 'erid of said pipe, said vent being so constructed and arranged where by a decrease in pressure within said space is adapted to move said cup upwardly relative to the pipe to permit air in said pipe to pass into said space beneath said lower edge and an increase in pressure Within said space is adapted to cause the roof to float higher on said liquid to raise the lower edge of the cup above the liquid to permit vapors in said space to enter the pipe.

2. In a floating roof tank having a roof adapted to float at various heights above the liquid level with varying vapor pressure in a space heneath the roof, a vent comprising; a substantially vertically arranged U-shaped pipe extending through said roof and having an exterior end open to the atmosphere and an interior end located in said space beneath the roof, said pipe having a first portion extending downwardly through said roof and a second portion extending upwardly to said interior end; an inverted cup over the interior end of said pipe, said cup being mounted for free vertical movement relative to said pipe and to said roof with variations in the height of said roof above said liquid and means attached to the roof for limiting the downward movement of said cup to prevent the cup from closing the interior end of said pipe, a sub stantially vertical cylinder formed in said roof and extending therethrough, the end of said cylinder above the roof being closed and the bottom of said cylinder comprising said limiting means and being foraminous and open to the tank below the normal height of the liquid with respect to the roof, said inverted cup being positioned within said cylinder and being free to move relative thereto with its lower edge being normally immersed in the liquid to provide a seal about the interior end or said pipe, said vent being so constructed and arranged whereby a decrease in pressure within said space is adapted to move said cup upwardly relative to the pipe to permit air in said pipe to pass into said space beneath said lower edge and an increase in pressure within said space is adapted to cause the roof to float higher on said liquid to raise the lower edge of the cup above the liquid to permit vapors in said space to enter the pipe.

FREDERICK D. MOYER. JOHN W. ALLEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,506,610 Booth Aug. 26, 1924 1,714,209 Bohnhardt May 21, 1929 1,975,144 Gates Oct. 2, 1934 2,117,829 Staber May 17, 1938 2,297,985 Rivers Oct. 6, 1942 2,384,147 Wiggins Sept. 4, 1945 

